Direct Numerical Simulations of Central ICE Guided by TRANSP Distribution Functions of NBI-ions in DIII-D Plasmas*

Ion cyclotron emission (ICE) is driven by strongly suprathermal ions, with spectral peaks at multiple ion cyclotron harmonics. Recent experiments on DIII-D (NF 59 (2019) 086011) using the upgraded ICE diagnostics (RSI 89 (2018) 10I102) have found spectral peaks at the local deuteron cyclotron frequency fci and its harmonics, at the edge and core of the plasma.

In this study, first principles 1D3V (one spatial and 3 velocity dimensions) kinetic simulations of ICE from DIII-D deuterium plasmas are performed using the fully gyro-resolved  particle-in-cell code EPOCH. Guided by the velocity distribution functions of the NBI ions from the TRANSP/NUBEAM module, the resulting simulations successfully reproduce the main findings of the experiments. To examine the temporal evolution and the spatial origin of central ICE spectral amplitudes in relation to local density and magnetic field, we have performed a set of ICE simulations for two different time slices and two vertical locations in DIII-D. This sheds light on the connection between the characteristics of the energetic ion velocity distribution function and the ICE spectra, creating a pathway to enhanced diagnostic exploitation of ICE in relation to fast ions and their radial transport.